The invention relates to copying machines of the type involving the movement of an original as a copy sheet such as a photosensitive paper or transfer sheet is moved, and more particularly, to such copying machines which permit a copying process at a magnification which is either equal to, or greater, or less than unity.
In conventional copying machines having a magnification of unity, the arrangement is such that an original can be moved with the same speed as a copy sheet, and the optical distance from the original to an optical system is maintained substantially equal to the optical distance from the latter to the copy sheet. When it is desired to utilize such a machine to perform a copying process at a varying magnification which is either greater or less than unity, it must satisfy additional requirements, which will be described below with reference to FIG. 1.
Referring to FIG. 1 which schematically shows a basic optical system in a copying process permitting a varying magnification, there is shown an in-mirror-lens 1 having a focal length of f, and the value of the magnification of the image on a copy sheet 3 with respect to the image of an original 2 is assumed to be m. When both the original 2 and the copy or photosensitive sheet 3 are placed on the same line l.sub.0, a copying process at a magnification of unity is achieved by locating the in-mirror-lens 1 at a distance of 2f from the line l.sub.0 (as shown in solid lines) and moving the original and the photosensitive sheet with an equal speed.
If a copying operation is desired at a reduced magnification or at a value of magnification less than unity, the photosensitive sheet 3 is left in position while the original 2 is disposed on a line l.sub.1 which is shifted from the line l.sub.0 by a distance of f(1/m - m) and the in-mirror-lens 1 is transposed to a position indicated by a phantom line which is transposed by f(1 - m) on the optical axis toward the line l.sub.0. Specifically, representing the distance between the lens 1 (shown in solid line) and the original 2 by a and the distance between the lens 1 and the photosensitive sheet 3 by b, the following relationships apply: EQU 1/a + 1/b = f, and m = b/a.
By rewriting, EQU a = f(1 + 1/m), and b = f(1 + m).
This indicates that the displacement of the original and the in-mirror-lens should be f(1/m - m) and f(1 - m), respectively. Assuming that the photosensitive sheet 3 has a width L.sub.1 across which it is slitwise exposed and which is at a spacing L.sub.2 from the optical axis, it follows from the optical relationships that the original 2 located on the line l.sub.1 should have a width L.sub.1 /m across which it is slitwise irradiated and which is at a spacing of L.sub.2 /m from the optical axis. Thus, by increasing the speed of movement of the original 2 by a factor 1/m (m &lt; 1) higher than that of the photosensitive sheet 3, a reduced image of a width L.sub.1 can be formed on the sheet 3 from an original having a width of L.sub.1 /m.
When a copying operation is desired at an increased magnification or at a magnification m&gt;1, the original 2 is disposed on a line l.sub.2 which is transposed from the line l.sub.0 toward the lens 1 by an amount equal to .vertline.f(1/m - m).vertline. while the lens is transposed to a position which is further removed from its position shown in solid line by an amount equal to .vertline.f(1 - m).vertline.. In addition, the speed of movement of the original 2 is reduced below the speed of movement prevailing at a magnification of unity, by a factor corresponding to the reciprocal of magnification 1/m (m &gt; 1). Then, an image of a width L.sub.1 /m (m &gt; 1) on the original 2 will be increased to a width of L.sub.1 on the sheet 3.
It will be appreciated from the foregoing discussions that in order to permit a copying operation at a varying magnification below and above unity, it is necessary that the original can be placed at a varying distance from the optical system, that the focussing lens such as the in-mirror-lens mentioned above can be moved through a selected distance along the optical axis, and that the original can be moved with a speed which depends on the magnitude of the magnification.